1. Field of the Invention
The present invention relates to a transparent substrate which is provided with at least one thin layer that is based on silicon nitride or silicon oxynitride. One application of the invention is the manufacture of so-called functional glazing assemblies used in buildings, vehicles, or as a plasma television screen. Another application which may be envisaged is the surface treatment of glass bottle containers. The invention also relates to a process for depositing these layers using a pyrolysis reaction.
2. Discussion of the Background
Within the context of the invention, the term functional glazing assembly should be understood to mean a glazing assembly in which at least one of its constituent transparent substrates is covered with a stack of thin layers so as to give it particular properties, especially thermal, optical, electrical or mechanical properties, such as scratch-resistance.
As an example, so-called low-emissivity thin layers are typically composed of a doped metal oxide, for example fluorine-doped tin oxide (F:SnO.sub.2) or tin-doped indium oxide (ITO), which may be deposited on glass using pyrolysis techniques. Once coated with a low-emissivity layer, the substrate mounted in a glazing assembly, in particular in a building, makes it possible to reduce emission, in the far infrared, to the outside of the room or vehicle interior through the said glazing assembly. By reducing the energy losses due in part to this radiation leakage, the thermal comfort is greatly improved, and particularly in the winter.
Alternatively, the substrate thus covered may be mounted in a double-glazing assembly; the low-emissivity layer being turned towards the gas-filled cavity separating the two substrates, for example, as the 3 face (the faces of a multiple-glazing assembly are conventionally numbered starting from the outermost face with respect to the room or the vehicle interior). The double-glazing assembly thus formed has enhanced thermal insulation, with a low heat-exchange coefficient, K, while maintaining the benefit of solar energy influx, with a high solar factor (i.e. the ratio of the total energy entering the room to the incident solar energy). On this subject, the reader may refer, in particular, to patent applications, EP-0,544,577, FR-2,704,543 and EP-0,500,445.
The low-emissivity layers are generally made of good electrical conductors. This allows the glazing assemblies, by providing suitable current leads, to be used as heating/de-icing glazing assemblies in motor vehicles, which application is described, for example, in EP-0,353,140.
Thin filtering layers, also called selective or anti-solar layers, are known which, when deposited on substrates mounted in a glazing assembly, make it possible to reduce the heat influx from solar radiation through the glazing assembly into the room or vehicle interior, by absorption/reflection. The layers may, for example, be layers of titanium nitride TiN (or titanium oxynitride), such as those obtained using a gas-phase pyrolysis technique and described in patent applications EP-0,638,527 and EP-0,650,938. The layer may also be a thin (less than or equal to 30 nm) reflective layer of aluminum, obtained by condensation of a metal vapor, CVD or the technique described in international patent application PCT/FR-96/00362 filed on Mar. 7, 1996, in the name of Saint-Gobain Vitrage.
The invention also relates to the techniques for depositing these various layers, and more particularly to those involving a pyrolysis reaction. These techniques consist in spraying "precursors", for example of an organometallic nature, which are either in the form of a gas, or in the form of a powder, or are liquids by themselves or else in solution in a liquid, onto the surface of the substrate which is heated to a high temperature. On coming into contact with the substrate, the said precursors decompose thereon, leaving, for example, a layer of metal, oxide, oxynitride or nitride. The advantage of pyrolysis resides in the fact that it allows direct deposition of the layer onto the glass ribbon in a line for manufacturing flat glass of the float type, continuously, and also in the fact that the pyrolysed layers have (in general) very good adhesion to the substrate.
The low-emissivity or filtering layers mentioned above frequently form part of a stack of layers and are, at least on one of their faces, in contact with another layer, generally a dielectric material having an optical and/or protective role.
Thus, in the aforementioned patent applications EP-0,544,577 and FR-2,704,543, the low-emissivity layer, for example made of F:SnO.sub.2, is surrounded by two layers of dielectric of the SiO.sub.2, SiOC or metal-oxide type, which layers have a refractive index and a thickness which are selected so as to adjust the optical appearance of the substrate, in particular in reflection, for example its color.
In patent application EP-0,500,445, also previously mentioned, the low-emissivity layer of ITO lies under a layer of aluminum oxide so as to protect it from oxidation and also, under certain conditions, to avoid having to subject it to a reducing annealing operation and/or to allow the coated substrate to be bent or toughened without adversely affecting its properties.
The TiO.sub.2 layer or the TiO.sub.2 /SiOC double layer which covers the TiN filtering layer in the aforementioned patent application EP-0,650,938 also protects the TiN from oxidation and improves its durability in general.
However, the integrity of the stacks of thin layers is important. Thus, it is necessary for them to display:
the ability to withstand chemical attack. It frequently happens that the transparent substrate, once coated with layers, is stored for quite a long period before being mounted in a glazing assembly. If the coated substrate is not carefully packaged in a sealed, and therefore expensive manner, the layers with which it is coated may be directly exposed to a contaminated atmosphere or may be subjected to cleaning by detergents which are not well suited to removing dust therefrom, even if the substrates are subsequently joined together in a double-glazing assembly or in a laminated glazing assembly with the deposited thin layers as the 2 or 3 face, and therefore protected. Moreover, apart from the storage problem, there is a disincentive to use the substrates as "monolithic glazing assemblies" or to arrange the layers as the 1 or 4 face in the case of multiple glazing assemblies, i.e., configurations in which the layers are exposed all year long to the ambient atmosphere if the stacks are susceptible to chemical corrosion; PA1 the ability to resist mechanical damage. For example, the transparent substrate, once coated with layers, may be used in configurations in which it is readily exposed to scratching damage. Consequently, on the one hand, the substrate no longer has a "correct" aesthetic appearance, since it is partially scratched, and, on the other hand, the durability of both the stack and the substrate is greatly diminished, because scratching may introduce possible sites of mechanical weakness, depending on the case. PA1 on the one hand, they are not necessarily sufficiently hard and are less durable, in particular when they are vacuum-deposited in order to, for example, endow a substrate provided with this single layer, or with a stack of thin layers comprising this layer, with a scratch-resistance function, and PA1 on the other hand, when they are deposited by pyrolysis, they are absorbent at wavelengths in the visible range, which is deleterious from an optical standpoint. PA1 Si: from 30 to 60%; PA1 N: from 10 to 56%; PA1 O: from 1 to 40%; and PA1 C: from 1 to 40%. PA1 Si: from 30 to 60%; PA1 N: from 10 to 56%; PA1 O: from 1 to 40%; and PA1 C: from 1 to 40%. PA1 SiO.sub.2 +Al.sub.2 O.sub.3 +ZrO.sub.2 .ltoreq.70% PA1 Al.sub.2 O.sub.3 +ZrO.sub.2 .gtoreq.2% PA1 Na.sub.2 O+K.sub.2 O.gtoreq.8% PA1 11%.ltoreq.MgO+CaO+BaO+SrO.ltoreq.30% PA1 Na.sub.2 O+K.sub.2 O.ltoreq.10% PA1 MgO+CaO+SrO+BaO&gt;11%, preferably &gt;15% PA1 glass/TiN and/or ZrN/thin layer according to the invention/SiOC and/or SiO.sub.2, the said layer according to the invention making it possible to have a much stronger interface between, on the one hand, the TiN layer and/or the ZrN layer and, on the other hand, the SiOC layer and/or the SiO.sub.2 layer. It also makes it possible to provide effective protection of the TiN and/or ZrN from the risk of surface oxidation either on the industrial line after deposition of the SiOC and/or SiO.sub.2 layer, or off the industrial line, for example when the substrate provided with the stack of layers, once it has been cut up, undergoes heat treatments of the bending/toughening or annealing type. Advantageously, the layer has a geometrical thickness of between 10 and 50 nanometers, the thin layer according to the invention has a geometrical thickness of between 5 and 20 nanometers and the SiOC and/or SiO.sub.2 overlayer has a geometrical thickness of between 30 and 100 nanometers; PA1 glass/Al/thin layer according to the invention, the aluminum reflective layer either having a small thickness (less than or equal to 30 nm) or having a greater thickness when the mirror function is desired, such as that described in the aforementioned international patent application PCT/FR-96/00362, the entire contents of which are hereby incorporated by reference, the thin layer according to the invention having both a role as oxidation-protection agent and a scratch resistance function. PA1 glass/SiOC/F:SnO.sub.2 or ITO/thin layer according to the invention. PA1 glass/thin layer according to the invention/TiO.sub.2.
There is therefore a continual search for a stack of layers having improved chemical and/or mechanical durability. However, these improvements must not adversely affect the optical properties of the assembly formed by the substrate and the stack of thin layers.
As mentioned previously, overlayers of dielectric material already exist which protect the underlying layers in the stack. In order to maintain integrity of an assembly that is exposed to intense or lengthy chemical corrosion, and/or to protect the possibly "weaker" underlying layers completely, patent application EP-0,712,815 describes a thin layer based on an oxide comprising silicon and a third element, for example a halogen of the fluorine F type, which facilitates the formation of a mixed silicon/aluminum structure.
The layer described above is particularly suitable for use as the final layer in stacks in which the functional layer is of the filtering or low-emissivity type on glazing assemblies, since it may fulfil an optical function such as optimizing the appearance in reflection, and may guarantee a degree of constancy of the appearance of the glazing assemblies over time.
However, the above-described layer is not necessarily capable of resisting mechanical damage, such as scratches, since does not have an extremely high hardness.
It is known that one type of hard thin layer most particularly designed to be durable and stable with respect to mechanical abrasion and/or chemical attack is a thin layer based on silicon nitride which may, as the case may be, contain a certain amount of oxygen and carbon.
Thus, one type of thin layer based on silicon nitride is known, this being deposited on a substrate by a gas-phase pyrolysis technique using two precursors, the silicon-containing precursor being a silane and the nitrogen-containing precursor being either inorganic, of the ammonia type, or organic, of the hydrazine type, in particular methyl-substituted hydrazine.
However, when the deposition is carried out using nitrogen-containing precursors of the ammonia type, the temperatures are too high (greater than 700.degree. C.) to be compatible with continuous deposition on a ribbon of silica-soda-lime glass in the chamber of a float bath since, at these temperatures, these standard glasses have not yet reached their dimensional stability.
In addition, the nitrogen-containing precursors of the hydrazine type have a degree of toxicity which makes their industrial application problematic.
It is also known to deposit a thin layer based on silicon nitride by the above-mentioned technique by using not two precursors but only one; one that contains both silicon and nitrogen, e.g., Si(NMe.sub.2).sub.4-n H.sub.n. However, the deposition rates that may be achieved are too low to exploit the deposition process on an industrial scale. Furthermore, the synthesis of the precursor is relatively complex and therefore expensive, and the respective proportions of the nitrogen-containing and silicon-containing precursor cannot be varied.
In addition, the known thin layers based on silicon nitride have certain drawbacks: